Crystal timeline from volcanic vents
30 April 2018
Studying volcanos is like detective work. The processes that kick-start an eruption occur deep underground and are impossible to observe directly, so volcanologists look for clues on the surface and work backwards using their knowledge of rock physics and chemistry.
Now, Teresa Ubide
at The University of Queensland, Australia and Balz Kamber at Trinity College
Dublin, Ireland have developed a new way to interpret chemical
clues from tiny clinopyroxene crystals that grow in the magma chambers of
volcanos. As these crystals grow, they build up layers similar to tree rings.
The layers contain information about how magma has changed over time, and allow
researchers to work out the timing of events that might trigger eruptions.
Kamber collected samples from Mount Etna in Sicily, the most active volcano in
Europe. Etna has shown increased activity since the 1970s, with eruptions occurring
not only from the central vents, but also from the sides of the volcano, which
is potentially more hazardous. The eruptions probably occurred soon after new
magma was injected into the chamber system, increasing pressure and causing
rapid magma ascent to the surface, carrying crystals with it.
flows we sampled at Etna for the paper are very recent (1974-2014) and detailed
geological maps are available,” says Ubide. “We looked for ‘fresh’ rocks,
without alteration or weathering, which contained abundant crystals.”
researchers collected samples from the lava flows of eight eruptions. Back in
the lab, they used a technique called laser
ablation mass spectrometry mapping to measure the amounts of trace elements,
particularly chromium, in the growth layers of 287 clinopyroxene crystals
present in the samples.
abundant in mafic (magnesium and iron rich) magmas and it is readily
incorporated into clinopyroxene crystals,” explains Ubide. “We assume that
crystals grow from the centre towards the rim, so if we find chromium-rich
zones close to the rim of the crystal, it suggests the arrival of mafic magma
just before the eruption.”
the thickness of the chromium-rich outer rims, the researchers estimated that
the eruptions tend to happen around two weeks after new magma arrives in
chambers ten kilometres below Etna’s surface. This new knowledge of the
timescale at which eruptions may be triggered could be extremely useful for future
- Nature Communications 9:326 (2018). doi: 10.1038/s41467-017-02274-w